High-frequency apparatus



April 8, 1952 R, R, LAW 2,591,947

HIGH-FREQUENCY APPARATUS Filed Dec. s1, 1949' 'fsf INVENTOR ORNEY Patented Apr. 8, i952 STATES PAT HIGH-FREQUENCY APPARATUS Russell R. Law, Princeton, N. l, assignor to Radio Corporation of America, a corporation oi' Delavare v This invention relates to ultra high frequency apparatus. More particularly it relates to improved ultra high frequency amplifiers and oscillators utilizing electron discharge devices and to an improved output coupling for preferred embodiments thereof.

As is known, it is common practice to employ electron discharge devices in circuits utilizing cavity resonators and wave-guides to produce oscillators and amplifiers, and' that the physical structure of these arrangements either provides for, or at least does not prevent, cooling of the anode.

Itis also desirable in some cases to cool the grid since it is usually fragile and therefore easily deformable by overheating. However in the past it has not been practical to provide such a cooling means because the grid supporting structure (for example the grid disc of a light-house triode) is usually contained within one or more metal housings where it cannot be reached by a cooling air blast.

Accordingly, it is an object of this invention to provide improvements for electron discharge device and cavity resonator assemblies of the character indicated so that means can be provided for cooling the grid of the discharge device.

Another object of the present Ainvention is to provide an amplifier or oscillator assembly comprising in combination a discharge device and .one or more cavity resonators coupled to elements thereof in which means are provided as an integral part of the assembly for aording improved cooling of the grid of the discharge device.

`As will be disclosed in detail, in accordance with my invention one way of attaining this object is to mount an annular resonator around the gridsupporting structure. It has the shape of a hollow ring of very large diameter with respect tothe shortest Wavelength for its operating band. A

large number of grid-cooling ns extend radially from the grid supportingi structure into the interior of the resonator where they can be cooled by a blast of air passing through the resonator. However certain diliculties arise because such a resonator is quite prone to m-ultimoding and can sembly of the character set forth above which in- 2 cludes a large-diameter annular cavity resonator and associated therewith an 'output circuit 'and transformer coupling means which does not increase the tendency of said resonator to multimoding.

In general according to one feature of the present invention a cavity resonator which surrounds the grid supporting structure comprises one or more walls which electrically are affectively continuous but physically are open to permit passage of a fluid cooling medium such as air, whereby this medium can be circulated within the resonator. An annular row of cooling vanes which are mounted outside of the tube envelope and extend from the periphery of a thermally-conductive grid-supporting structureA into the path of said cooling medium extend into the physical structure of the resonator. These vanes are so closely spaced that their edges effectively denne interior electrical surfaces of the resonator. The row of grid-cooling vanes may extend into the structure of the resonator between two physically open end Walls of the resonator or it may be positioned opposite one such end wall and itself serve as the other.

In the drawing:

Fig. l is an end view of a plural-cavity electron discharge device, embodying the invention;

Fig. 2 is a longitudinal sectional view taken on the line 2 2 of Fig. 1; and

Fig. 3 isa longitudinal sectional View of an alternative embodiment of the invention.

An ultra high frequency amplifier is represented in Figs. 1 and 2 of the drawing. As best shown in Fig. 2 it comprises an indirectly heated cathode lil having anat circular emissive coating i l. Supported adjacent to the coating i i and closely spaced therefrom is a flat circular control grid i2 which is supported by its edges in a central opening in the righthand metal wall i3 of a cathodegrid cavity resonatori5. This wall and preferably all of the Walls of the resonator i5 should be made of conductivematerial such as copper (whether or not theyhave their interior surfaces silver plated) tothe end that means isprovided for conducting heat away from thegrid l2.

Since the gridA l2 is an integraly part of the resonator I5 and since in the operation of the amplifier-,it is necessary toestablish an appropri ate direct potential bias between the cathodeand the control grid, it is essential to providedirect current insulation between the .cathode thimble i6 and the body ofthe resonator iE. However, it must be remembered in this connection thati the inner walls of thev cavity must not' bev electrically thimble I6 coaxially within a tubular extension.

I'l which protrudes leftward from the left wall I8 of the resonator I and may be in the form of an extrusion drawn from the center of that wall or of a separate part attached thereto.

Fitted tightly into the very small space between the thimble I6 and the sleeve Il is a cylindrical insulating shim or spacer I9 which preferably should be of a material, such as mica, having a high dielectric constant. In the arrangement shown in Fig. 2 it is not necessary that the shim I9 t so accurately as to form a vacuum seal between the outside of the thimble IB and the inside of the Sleeve I1. Instead a small glass bulb 2i! is placed over the left end of the entire cathodemounting assembly and its edges are sealed to the outside of the sleeve l1 as shown. Sealed through the left end of this bulb are a pair of leads 22, 23 for the cathode heater 24 (these leads and the heater are insulated from the cathode thimble by a means, not shown, such as by a coating of aluminum oxide) and a lead 25 which extends from the cathode thimble I6.

An anode 2l consisting of a thick circular disc of electrically and thermally conductive material such as copper is supported on the right hand side of the outside surface of the wall I3 with ap; propriate Spacing therefrom so that the coating I I the grid I2 and the left surface of the anode 2l comprise an ultra-high frequency triode. The anode 21 is supported in this position by a ring of glass 28 which forms a vacuum seal between the wall I3 and the anode 2l. From the foregoing it is apparent that all of the space within the resonator I5, the bulb 20 and the cathode thimble I6, as well as the space between the resonator and the anode is sealed from the outer atmosphere so that it may be pumped down to a hard vacuum. A means for coupling an input signal to the resonator I5 is provided at 30, it having the form of an inductive loop which is mounted within the resonator and is connected to a coaxial fixture on the outside thereof.

' Resonator I5 may be considered as comprising one lumped capacitance between the coating Il and the grid l2 and a number of parallel shunt inductances. The inductances are afforded by conductive paths which extend axially along the outside of the thimble I6 between the coating Il and the wall I8; radially along the inside surface of the Wall I8 between the cathode thimble and the inside of the cylindrical wall 2I of the resonator; axially along the inside of the wall 2l between the walls I3 and I8; and radially along the inside of wall I3 between the wall 2| and the grid I2. In the operation of this amplifier an electric eld which changes in accordance with the input signal will be established across the capacitive gap between the coating I I and the grid I2 to control the discharge current of the triode.

A grid-anode cavity resonator 32 is shown which electrically is very similar to resonator I5 but physically is quite different from it. The wall of resonator 32 which electrically corresponds to' the wall I3 of the resonator I5 is composed of a plurality of fins 33 which extend radially from the cylindrical periphery of anode 2l to the inner surface of a metallic cylindrical rim 35 to each of which they are connected for example with silver solder, to form a rigid structure and to provide low impedance electrical and thermal conduction from the anode to the rim. The fins 33 are so closely spaced that even for the shortest wavelength at which this amplifier is intended to operate their leftward-facing edges will define an electrically unbroken surface corresponding to the inner surface of the wall I3. The cylindrical outer wall of resonator 32 consists of a large-diameter cylinder 36 in the right end of which the rim 35 is mounted. A thin dielectric spacer 3l is fitted between the cylinder 3S and the rim 35 to provide a direct current open circuit between the anode and the grid and a radio frequency by-pass across it.

In the operation of this amplifier sources of direct potentials for the grid and the anode may be individually connected to the structural assemblies which respectively immediately surround these elements.

A second group of fins 38 are arranged in an annular row around the outside of the resonator I5. From the foregoing it is apparent that in the operation of this amplifier' heat generated at the grid I2 will be conducted along the wall I3, thence to the cylindrical wall 2| and thence to the fins 33 from which it can be dissipated by a blast of cold air directed as indicated by the arrows 40. Because of the close spacing of the fins 38 their inwardly facing edges 4I, 42 and 43 are effective to dene some of the internal electrical boundaries of the resonator 32. Since in the preferred mode of operation for the resonator 32 (i. e., in

, the Zero mode) radio frequency currents will tend will be operative but may even have a desired high value of Q.

Means for withdrawing energy from the output resonator 32 is shown at 45 in the form of an inductive loop mounted within the resonator and connected to an external coaxial fixture by a conductor which extends out of the resonator between two of the vanes 38.

The embodiment of Fig. 3 resembles that of Fig. 2 in many respects. However in it the resonators are of the annular type which of course may be of very large diameter in terms of wavelength and therefore particularly susceptible to multimoding; it includes a means for coupling the large-diameter resonator 32' to a small-diameter coaxial output line without disturbing the cylindrical symmetry, of that resonator (and thereby increasing its tendency to multimoding) and it is modified to act as an oscillator rather than an amplier.

As will be understood by those familiar with the art in the sort of arrangement of annular resonators which is shown in Fig. 3, certain space such as the space between the two brackets m, y, is dead space, i. e., space which has no material effect on the operation of the resonators and does not materially add to the volume of their resonant spaces, this being truc -because of the negligible amount of capacitance between the set-back surfaces in the central re- 'gions of the cathode and the anode. It will be noted that because of the modified form of the Vcathode thimble IB the emissive coating Il' is annular rather than circular and the heater 24 Itis known to use transformers connected betwo unequally-proportioned coaxial lines, each of which lies along an extension of the axis of the other, which transformers comprise tapered is wound as a large-diameter spiral rather than `5 inner and outer conductors each acting alone to provide a smooth transition between the correas a small helix.

Besides the novel coupling means shown herein an 'additional factor contributing to the stability of this oscillator is the fact that the abovedescribed physically-open type of structure,

`which is also used for some of the walls of resonator 32', tends to confine the flow of current in certain predetermined directions.

Obviously the `operating frequency of a resonator like resonator l5 of Fig. 2 will be increased without increasing its overall diameter if vit is .modified to have the annular form shown for resonator I5 in Fig. 3. This is due to the fact vthat the modification results in a considerable reduction in the distance measured around the inside of a cross-section of the resonator taken in a plane normal to the annular axis of the resonator from one side of the capacitive gap to Y. the other, i. e., from the ernissive coating to the grid. Accordingly, in Fig. 3 the diameter of the annular axis of the resonator' l5' may be large or even very large with respect to the wave- 1 length corresponding to the operating frequency of the oscillator. It is assumed that resonator 32 will be designed with a resonant frequency corresponding to that of resonator l5'.

Feedback from the cavity 32' to the cavity l5 takes place through a plurality of equally spaced R. F. windows 55] each of which consists of an opening in a common wall between the resonators 32 and l5 and a vacuum-tight seal of dielectric material across the opening. Since small openings will usually provide sufficient feedback and since these openings are evenly spaced, they will not materially disturb the symmetry of the large-diameter annular cavity 32'.

A However, if desired, the feedback means may be made with the even more symmetrical form of a very `narrow slot extending all the way around the cylindrical wall 2|.

In the Fig. 3 embodiment each of the ns 38 of the Fig. 2 embodiment is replaced by `two fins, 52, 53 which may be considered as formed from this n 38 by Acutting away an appropriate portion thereof so that the resonant space within the resonator 32' extends to the wall 2|' with the result that part of it becomes a common wall .in which the feedback means may be located and so that the resonant space also extends to a cylindrically symmetrical opening 55 through which output energy may radiate over a transformer arrangement 56 into an output line 51. This includes a large-diameter concentric line 59 whose inner and outer conductors 60 and 6I are of such sizes that the space 'between them coincides with the opening 55 and that the outer conductor 62 of line 51 ts within the inner conductor 6I with a considerable amount of clearance all the way around.

As is known, the surge impedance of a concentric line is not solely a function of 'its overall largeness of diameter but also of the ratio of the inside diameter of its outer conductor to the outside diameter of its inner conductor. Therefore it should be borne in mind that the surge impedances of the respective lines 59 and 51 will not necessarily have a disparity corresponding to that between the overall diameters of these lines. Generally speaking, however, the smaller of the two lines will usually have the lower impedance.

sponding (inner or outer) conductors of the two lines and both acting together to provide a smooth transition between the inter-conductor spaces of the two lines. However, in certain installations the extension of the length of the circuit which this necessitates may be undesirable. To avoid this diiculty there is shown herein a transformer section 85 which extends radially between cylindrically symmetrical windows formed respectively in the inner conductor 1 6| ofthe line 59 and the outer conductor 62 of the line 51. Assuming a higher impedance for -line 59 than line 51 the transformer section 55 should taper outward toward the point Where it r., is .coupled to the window 6E of the inner conducthe oscillator to move the window 5t along a ooaxial stub formed 'between the conductorst and 6l. This stub is completed by a shorting element 10 which is inserted into its open left hand end and can be moved leftward and rightward in it. In the operation of this oscillator the shorting .element 10 is moved to match line 59 to the oscillator. This will set up a certain standing wave distribution within the coaxial stub 59. Thereafter the assembly comprising the line 51, the transformer section 65, and the conductor 6I is moved axially of the oscillator' so that an impedance match is attained between the load as seen through the opening 65 looking inward into the transformer G5 and the source as seen therethrough looking outward into the stub. It will be noted that in the embodiment of Fig. 3 the cylindrical outer wall 2l of the resonator 'I5' includes an extension 2|" which serves as the male Aportion of a trombone arrangement which is completed by the inner conductor 6I as shown in the drawing. In order to assure satisfactory contact where conductor 6I slides over extension 2l the conductor El may be axially slotted to form a plurality of spring fingers' according to known techniques. Similar ngers may also be used in forming the shorting means 1c.

If Vperchance the two lines 51 and 59 should have the same surge impedance despite the disparity between their overall diameters it would not be necessary to provide any radial taper for the transformer section 65.

It is conceivable that in some particular embodiments of the present invention, the small diameter line .may actually have a higher impedance than the larger line due to the use of wide spacing between itsconductors. In such a case, if dee sired, the taper ofthe transformer section may be reversed so that in effect it is built up of two frusta-cones whose large ends are nearest together.

Moreover, it is possible within :the scope of the present invention to utilize the transformer for feeding and matchingto a cylindrical waveguide.

The advantage of the present arrangement o its not increasing any tendency of a large-diameter annular resonator to multimoding will not be affected by the mode in which the physicallysmall output system is excited or by the fact that this is different from the fundamental mode of that resonator. Y

While certain specific embodiments have been illustrated and described, it will be understood that various changes and modifications may be made without departing from the spirit and scope of the invention.

What I claim as new is: v -v 1. A high frequency apparatus comprising an evacuated envelope, a pair of electrodes each having a surface which is cooperatively spaced'from a surface of the other and located within the envelope, a respective means including a metallic surface external to said envelope for conducting heat from each electrode'through theenvelope to said metallic surface, a row of external cooling fins extending from each of said metallic surfaces, a hollow cylindrical memberin electrical contact with the fins of each row, some of the inside surface of said member and inwardly facing edges of the fins of said rows defining interior surfaces of a cavity of a resonator.

2. A high frequency apparatus comprising' a discharge device includingan evacuated envelope, and therewithin a cathode, a control grid, and an anode surface; means including a metallic surface external to said envelope for conducting heat from said grid through said envelope to said metallic surface; a row of external cooling-fins extending from said metallic surface; a hollow conductive member' surrounding. at least ,a portion of said row of fins and forming therewith a cavity resonator.

3. A high frequency apparatus comprising an electron discharge device having a rst electrode and radially directed ns electrically connected to said electrode, said device having a second electrode spaced from said first electrode and radially directed fins electrically connected to 'said second electrode, and conductive means surrounding said ns and forming therewith a cavity resonator, said iins being closely spaced to form walls electrically closed to radio frequency currents for the resonant frequency of the resonator but physically open to a coolant passing into and out of said resonator.

4. A discharge device comprising an evacuated envelope, within the envelope an electron emissive surface, a control grid and an electron receiving surface positioned in. the order named along a discharge path with the grid 'extending transversely to and across said path, a thermally conductive structure surrounding and supporting the grid, a plurality of heat dissipative ns arranged in an annular row and extending radially from said structure into a cooling medium outside of said envelope, a cavity resonator physically surrounding at least a portion of the annular row of fins, the ns being so closely spaced and disposed in such directions that edges thereof whichv ductive structure surrounding and supporting' unbroken conductor the grid, a plurality of heat dissipative fins arranged in an annular row and radially extending from said structure into a cooling medium outside of said envelope, a first cavity resonator including said thermally conductive structure as at least a part of one of its walls and having a 'capacitive gap between said electron emissive surface and said grid, a second cavity resonator surrounding at least a portion of said first cavity resonator and of said annular row of fins, the fins being so closely spaced and disposed in such .directions that outer edges thereof which face toward the inside of the second resonator effectively define continuously-radio-frequencyconductive interior boundary surfaces thereof,

'said second resonator having a capacitive gap between said grid and said electron receiving surface.

, 6. An electron discharge device as in claim 5 in which an outer Wall of said second resonator ,comprises a conductive structure having a plurality of openings each of which is of small size with respect to one wavelength of the lowest frequency of the operating band for said resonator whereby said wall will be physically per- 4me'able to a fiuid cooling medium whereas elec- 'said tubular wall.

8. An ultra high frequency system comprising a large diameter annular cavity resonator of cylindrical symmetry, coaxial therewith a small diameter coaxial output line for carrying R. F. energy between the cavity resonator and another portion of the system, a circular window formed in the resonator concentric with its axis pro- .viding part of a cylindrically symmetrical path for the transfer of radio frequency energy between the interior of the resonator and said small diameter line, a large diameter coaxialtranslmission line so proportioned that the spacing between its inner and outer conductors coincides with said circular opening and means for attaching one end of said large diameter line to said opening, the small line being coaxial with the large line and inserted within the inner conductor thereof, an opening of cylindrical symmetry in the inside conductor of the large line vand in ralignment therewith a similar opening in the outer conductor of the small line, a transformer electrically interconnecting the large and small diameter lines for matching the impedances thereof, said transformer comprising a transition section extending radially between the respective openings of cylindrical symmetryof said inner conductor of the large line and said outer conductor of the small line.

9. An ultra high frequency system as in claim 8 in which the characteristic impedances of said two lines are unequal and said transition section is tapered radially for matching impedances which each presents to the other.

10. An ultra high frequency system as. in

` claim 8 further comprising means for terminating the other end of said large diameter line lin a reflective impedance substantially unequal to the characteristic impedance of said line to cause it to act as a resonant stub and to set up standing waves therein during the operation of the system, and means for moving along said stub the opening of cylindrical symmetry which is formed in its inner conductor, said last-mentioned means comprising means for moving the transition section together with said opening to maintain coupling therebetween for all positions thereof.

1l. A high frequency system comprising a large ldiameter coaxial transmission line, the inner conductor of said line having an opening of cylindrical symmetry, a small diameter hollow conductor also having an opening of cylindrical symmetry and being inserted within the inner conductor of the large diameter line to a point where said openings are in predetermined alignment, and a transition section formed of a pair of oppositely disposed disc-like members each having inner and outer peripheries respectively terminating at corresponding sides of said respective openings for electrically interconnecting said respective openings.

12. A high frequency apparatus including a tuned circuit element of annular symmetry as the figure of revolution of a closed pattern about a center outside of said pattern, the tuned element enclosing space adapted to be resonant in a predetermined frequency range, said circuit element having outer and inner` curved walls 10 whose respective interior surfaces face each other across said space the former facing the latter in directions which are radial toward said center and the latter facing the former in opo posite directions, one of said curved Walls having an opening of cylindrical symmetry, a hollow cylindrical conductor having a diameter which is diierent than that of either of said curved walls and is more nearly equal to that of the curved wall having said opening than tothe other, said hollow conductor being coaXially disposed with respect to the last-mentioned curved wall and axially positioned with respect thereto with their respective openings in predetermined registry, and a transition section formed of a pair of oppositely disposed disc-like members each having inner and outer peripheries respectively interconnecting corresponding sides of said registered openings.

RUSSELL R. LAW.,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,411,299 Sloan Nov. 19, 1946 2,456,579 Burnside Dec. 14, 1948 2,484,643 Peterson Oct. 11, 1949 

